The Rig Veda is a group of poems that people in India first sang
and recited maybe about 1500 BC, soon after the Indo-Europeans arrived in India. People passed down these poems by reciting them out loud for hundreds of years, adding some and forgetting some. By about 1000 BC, the Rig Veda reached its final form, and then people finally wrote it down in Sanskrit in the Guptan period,
about 500 BC. The Rig Veda is one of the most sacred
texts of Hinduism.

The Rig Veda tells the story of Prajapati, the first
god who created the world. Prajapati means “Lord of Creatures”.
Prajapati was sacrificed to himself by the younger gods Indra, Agni,
and Varuna, and out of his body the whole universe was made. The Rig
Veda says that each of Prajapati’s other parts turned into a different
group of people, so that Indian people thought of themselves as belonging
to one of four castes, or groups.
This idea of caste seems to be an Aryan
idea.